Methods for graphene formation using microwave surface-wave plasma on dielectric materials

ABSTRACT

A method of forming graphene layers is disclosed. A method of improving graphene deposition is also disclosed. Some methods are advantageously performed at lower temperatures. Some methods advantageously provide graphene layers with lower resistance. Some methods advantageously provide graphene layers in a relatively short period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/737,868, filed Sep. 27, 2018, the entire disclosure of which ishereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to methods fordepositing or forming graphene. Some embodiments of the disclosurerelate to methods for forming graphene layers on a dielectric substrate.Some embodiments relate to methods for improving the substrate surfacequality or deposition parameters while depositing graphene.

BACKGROUND

Graphene has been attracting tremendous amounts of attention insemiconductor manufacturing as a result of its outstanding optical andelectrical properties. Due to its unique 2D honeycomb-shaped lattice andone atomic layer structure, graphene, a monolayer of carbon atomsarranged in a hexagonal lattice, has extraordinary potential for thefuture of the electronics industry. Graphene is the thinnest material,with a thickness of one carbon atom, about 3.35 angstrom. Therefore,graphene has the highest specific surface area (SSA) recorded amongcarbon materials. This high SSA provides the promising attribute thatgraphene is able to store more energy than other carbonaceous materials.In addition, the delocalized electrons in graphene sheets are able totravel at high speeds with intrinsic mobility of about 2-2.5×10⁵ cm²/vs;thereby helping to transport current efficiently. Due to its thinthickness and high electron mobility, graphene can be used as areplacement for traditional metal barrier layers in next generationsemiconductor devices because the resistance of metal lines gets higherand higher as their thickness and dimensions continue to shrink.Graphene also demonstrates high optical transparency, which can be usedin flexible electronics, for example in smart watch applications.

Traditional graphene CVD growth requires high temperature (>1000 C) andmetal foils as catalysts. At this high temperature, most materials usedin the electronic applications could be damaged. In addition, the metalfoils need to be removed after graphene growth. The transfer process iscostly, and could damage graphene layers and cause metal contaminationas well. For this reason, low temperature growth without using metalcatalysts is highly desirable.

Currently, chemical vapor deposition (CVD) with metal catalysts is usedto grow graphene films. Although high quality graphene films can bedeposited by CVD growth, it requires high growth temperature, typically800-1000° C. or more. This is not compatible with current integrationflows in the semiconductor industry because the metal lines and low kfilms on device wafers cannot tolerate such high temperatures. Inaddition, graphene deposited by high temperature CVD also needs to betransferred from the metal foils. The transfer process is costly and canlead to damage of the film, defects in the film, and metalcontamination. Therefore high temperature CVD by known methods isneither convenient nor feasible for industrial applications. So, directgrowth on arbitrary substrates without the use of metal catalysts atrelatively lower temperatures is highly desirable.

Accordingly, there is a need for improved methods of depositing graphenelayers.

SUMMARY

One or more embodiments of the disclosure are directed to a method offorming a graphene layer. The method comprises exposing a substratesurface comprising a dielectric material to a microwave surface-waveplasma comprising hydrocarbon and hydrogen radicals to form a graphenelayer.

Additional embodiments of the disclosure are directed to methods ofimproving graphene deposition. The methods comprise exposing a substratesurface to an oxygenating plasma to improve one or more substratesurface quality or deposition parameter.

Further embodiments of the disclosure are directed to methods of forminga graphene layer. The methods comprise pretreating a substrate surfacecomprising a dielectric material by exposing the substrate surface to anoxygenating plasma. The oxygenating plasma comprises O₂. The substratesurface is exposed to a microwave surface-wave plasma comprisinghydrocarbon and hydrogen radicals to form a graphene layer by ignitingacetylene and hydrogen gas. The oxygenating plasma and the microwavesurface-wave plasma have a peak power of less than or equal to about 20kW. The substrate surface is maintained at a temperature of less than orequal to about 750° C. The graphene layer comprises about 5 to about 10monolayers of graphene and is formed in a period of less than or equalto about 2 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 is a flowchart of a method for forming a graphene layer accordingto one or more embodiment of the disclosure; and

FIG. 2 is a flowchart of a method for improving graphene depositionaccording to one or more embodiment of the disclosure.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the disclosure, it isto be understood that the disclosure is not limited to the details ofconstruction or process steps set forth in the following description.The disclosure is capable of other embodiments and of being practiced orbeing carried out in various ways.

As used in this specification and the appended claims, the term“substrate” refers to a surface, or portion of a surface, upon which aprocess acts. It will also be understood by those skilled in the artthat reference to a substrate can also refer to only a portion of thesubstrate, unless the context clearly indicates otherwise. Additionally,reference to depositing on a substrate can mean both a bare substrateand a substrate with one or more films or features deposited or formedthereon

A “substrate” as used herein, refers to any substrate or materialsurface formed on a substrate upon which film processing is performedduring a fabrication process. For example, a substrate surface on whichprocessing can be performed include materials such as silicon, siliconoxide, strained silicon, silicon on insulator (SOI), carbon dopedsilicon oxides, amorphous silicon, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, semiconductorwafers. Substrates may be exposed to a pretreatment process to polish,etch, reduce, oxidize, hydroxylate, anneal, UV cure, e-beam cure and/orbake the substrate surface. In addition to film processing directly onthe surface of the substrate itself, in the present disclosure, any ofthe film processing steps disclosed may also be performed on anunderlayer formed on the substrate as disclosed in more detail below,and the term “substrate surface” is intended to include such underlayeras the context indicates. Thus for example, where a layer or partiallayer has been deposited onto a substrate surface, the exposed surfaceof the newly deposited layer may also be described as the substratesurface.

Embodiments of the present disclosure relate to methods for forminggraphene layers. Further embodiments of the disclosure relate to methodsfor improving graphene deposition processes. Some embodiments of thedisclosure advantageously provide methods for forming graphene layers atlower temperatures. Some embodiments of the disclosure advantageouslyprovide methods for forming graphene layers of a predetermined thicknessin a shorter period of time. Some embodiments of the disclosureadvantageously provide methods for forming graphene layers with lowerresistance.

Referring to FIG. 1, a method 100 for forming a graphene layer is shown.The method 100 begins at operation 104 by exposing a substrate surfaceto a microwave surface-wave plasma.

The substrate surface is the exposed surface of a substrate material. Insome embodiments, the substrate material is a dielectric material. Insome embodiments, the dielectric material comprises one or more ofsilicon, silicon oxide, silicon nitride or glass. As used herein, termssuch as “silicon oxide” and “silicon nitride” refer to materialscomprising silicon and oxygen or silicon and nitrogen. “Silicon oxide”and “silicon nitride” should not be understood to imply anystoichiometric ratio. Stated differently, a dielectric materialcomprising silicon oxide or silicon nitride may be stoichiometric ornon-stoichiometric, silicon-rich or silicon-poor.

In some embodiments, the substrate material comprises substantially nometal atoms. In some embodiments, the substrate material does notconsist essentially of metal atoms. As used herein, a material which“consists essentially of” metal atoms comprises greater than 98%, 99%,99.5% or 99.9% metal atoms on an atomic basis.

The microwave surface-wave plasma is also referred to herein as simply“the plasma”. In some embodiments, the plasma has a peak power of lessthan or equal to 50 kW, less than or equal to 40 kW, less than or equalto 30 kW, less than or equal to 25 kW, less than or equal to 20 kW, orless than or equal to 15 kW. In some embodiments, the plasma has afrequency in the range of about 300 MHz to about 300 GHz, or in therange of about 1 GHz to about 140 GHz, or in the range of about 2 GHz toabout 50 GHz, or in the range of about 3 GHz to about 30 GHz, or about2.45 GHz or about 5.4 GHz.

Without being bound by theory, it is believed that the microwavesurface-wave plasma advantageously provides a plasma which has a highradical density but a low energy. It is believed that the higher radicaldensity favors high chemical reactivity and that the low energyminimizes ion bombardment of the substrate and the associated damage anddefects.

In some embodiments, the plasma has a radical density (radicals/cm³) ofgreater than or equal to about 10¹², greater than or equal to about10¹³, greater than or equal to about 10¹⁴, greater than or equal toabout 10¹⁵, greater than or equal to about 10¹⁶, or greater than orequal to about 10¹⁷ radicals/cm³. In some embodiments, the plasma has anenergy of less than or equal to about 25 eV, less than or equal to about20 eV, less than or equal to about 15 eV, less than or equal to about 10eV, less than or equal to about 8 eV, less than or equal to about 6 eV,less than or equal to about 5 eV, less than or equal to about 4 eV, lessthan or equal to about 2 eV, or less than or equal to about 1 eV. Insome embodiments, the plasma has a plasma energy in the range of about0.1 eV to about 50 eV, or in the range of about 0.5 eV to about 25 eV,or in the range of about 1 eV to about 10 eV.

The plasma comprises hydrocarbon and hydrogen radicals. In someembodiments, a hydrocarbon gas and a hydrogen-containing gas are ignitedto form the plasma comprising hydrocarbon and hydrogen radicals. In someembodiments, the plasma is ignited in a region adjacent to the substratesurface within a processing chamber.

The hydrocarbon gas can be any suitable gas comprising carbon atoms andhydrogen atoms. In some embodiments, the hydrocarbon gas consistsessentially of carbon atoms and hydrogen atoms. In some embodiments, thehydrocarbon gas has less than or equal to 6 carbon atoms. In someembodiments, the hydrocarbon gas comprises one or more of methane,ethane, propane, butane, ethylene, propene, or acetylene. Without beingbound by theory, it is believed that the hydrocarbon radicals primarilyreact on the substrate surface to form the graphene layers.

The hydrogen-containing gas can may any suitable gas capable ofgenerating hydrogen radicals. In some embodiments, thehydrogen-containing gas comprises or consists essentially of hydrogengas (H₂). Without being bound by theory, it is believed that thehydrogen radicals etch any amorphous carbon generated by the hydrocarbonradicals from the substrate surface. In some embodiments, the graphenelayers comprise substantially no amorphous carbon.

In some embodiments, the hydrocarbon gas and the hydrogen-containing gasare delivered to the processing chamber sequentially. In someembodiments, the hydrocarbon gas and the hydrogen-containing gas aredelivered to the processing chamber simultaneously. In some embodiments,the hydrocarbon gas and the hydrogen-containing gas are mixed prior toentering the processing chamber. In some embodiments, the hydrocarbongas and the hydrogen-containing gas are delivered with an inert carriergas. In some embodiments, the carrier gas comprises argon.

The temperature of the substrate surface may be controlled duringformation of the graphene layer. In some embodiments, the substratesurface is maintained at a temperature of less than or equal to about800° C., less than or equal to about 750° C., less than or equal toabout 700° C., less than or equal to about 650° C., less than or equalto about 600° C., less than or equal to about 500° C., less than orequal to about 400° C., less than or equal to about 300° C., less thanor equal to about 200° C., less than or equal to about 100° C., lessthan or equal to about 50° C., or less than or equal to about 25° C. Insome embodiments, the substrate surface is maintained at a temperaturein a range of about room temperature (e.g., 25° C.) to about 800° C.,about 300° C. to about 800° C., or about 600° C. to about 800° C.

Without being bound by theory, it is believed that CVD processes forforming graphene layers are typically performed at temperatures inexcess of 1000° C. The present disclosure provides methods fordepositing graphene layers at a lower temperature. It is believed thatthese lower temperatures are more compatible with the thermal budget ofelectronic devices during manufacture.

Returning to FIG. 1, the formation process at operation 104 may beperformed until a predetermined thickness of graphene has been formed.At operation 106, the thickness of the formed graphene layer isevaluated to determine if it has reached the predetermined thickness. Ifnot, the method 100 returns to operation 104 for further formation. Ifso, the method 100 ends.

In some embodiments, operation 106 may be able to be conducted whileoperation 104 is still being performed. Alternatively, in someembodiments, operation 104 may be ceased before and/or during operation106.

In some embodiments, the graphene layer formed by the disclosed methodcomprises less than or equal to about 1, less than or equal to about 2,less than or equal to about 5, less than or equal to about 10, less thanor equal to about 20, gr less than or equal to about 25, or less than orequal to about 30 monolayers of graphene. In some embodiments, thegraphene layer formed by the disclosed method comprises in the range ofabout 0.5 to about 25 monolayers, or in the range of about 0.5 to about10 monolayers, or in the range of about 1 to about 5 monolayers, or inthe range of about 5 to about 10 monolayers of graphene. In someembodiments, the graphene layer formed by the disclosed method has athickness of less than or equal to about 3 Å, less than or equal toabout 5 Å, less than or equal to about 10 Å, less than or equal to about15 Å, less than or equal to about 20 Å, less than or equal to about 25Å, less than or equal to about 30 Å, less than or equal to about 40 Å,or less than or equal to about 50 Å.

In some embodiments, the method 100 is capable of being performed in arelatively short time period. In some embodiments, the graphene layer isformed in a period of less than or equal to about 15 minutes, less thanor equal to about 10 minutes, less than or equal to about 5 minutes,less than or equal to about 2 minutes, or less than or equal to about 1minute.

In some embodiments, the resistance of the graphene layer formed by thedisclosed method is relatively low. In some embodiments, the graphenelayer has a resistance of less than or equal to about 2000 ohm/square,less than or equal to about 1000 ohm/square, less than or equal to about500 ohm/square, less than or equal to about 400 ohm/square, less than orequal to about 300 ohm/square, less than or equal to about 250ohm/square, or less than or equal to about 200 ohm/square.

Referring to FIG. 2, a method 200 of improving graphene deposition isshown. The method 200 comprises, at 202, exposing a substrate surface toan oxygenating plasma to improve one or more substrate surface qualityor deposition parameter. Next, at 204, a graphene layer is formed on thesubstrate surface.

In some embodiments, the method 200 can be incorporated into method 100as optional operation 102. In some embodiments, method 200 is practicedapart from method 100 with a different graphene formation process.

The substrate surface for method 200 may be comprised of any suitablesubstrate material, including dielectrics and metals. In someembodiments, the substrate material is a dielectric material. In someembodiments, the substrate material consists essentially of a metal. Insome embodiments, the substrate material comprises copper.

The oxygenating plasma may comprise any suitable materials capable ofelectrochemically oxidizing the substrate surface. Without being boundby theory, it is believed that oxidizing the substrate surface removesany hydrogen terminations as well as any other potential contaminants.The treated substrate surface is able to provide a smooth, clean surfacefor graphene formation. In some embodiments, the oxygenating plasmacomprises O₂ or H₂O.

The oxygenating plasma may be generated by any suitable plasma source.In some embodiments, the oxygenating plasma comprises a microwaveplasma. In some embodiments, the oxygenating plasma comprises a remotelygenerated plasma. In some embodiments, the oxygenating plasma comprisesa direct plasma. In some embodiments, the oxygenating plasma comprises aconductively coupled plasma (CCP). In some embodiments, the oxygenatingplasma comprises an inductively coupled plasma (ICP).

The temperature of the substrate surface may be controlled duringexposure to the oxygenating plasma. In some embodiments, the substratesurface is maintained at a temperature of less than or equal to about800° C., less than or equal to about 750° C., less than or equal toabout 700° C., less than or equal to about 650° C., less than or equalto about 600° C., less than or equal to about 500° C., less than orequal to about 400° C., less than or equal to about 300° C., less thanor equal to about 200° C., less than or equal to about 100° C., lessthan or equal to about 50° C., or less than or equal to about roomtemperature (e.g., 25° C.). In some embodiments, the substrate surfaceis maintained at a temperature in a range of about room temperature(e.g., 25° C.) to about 800° C., about 300° C. to about 800° C., orabout 600° C. to about 800° C.

In some embodiments, the oxygenating plasma has a peak power of lessthan or equal to 50 kW, less than or equal to 40 kW, less than or equalto 30 kW, less than or equal to 25 kW, less than or equal to 20 kW, orless than or equal to 15 kW.

In some embodiments, the improved substrate surface quality is increasedsmoothness. In some embodiments, the improved substrate surface qualityis decreased hydrogen concentration. In some embodiments, the improvedsubstrate surface quality is decreased contamination. These improvementsare measured relative to a substrate surface which has not been treatedwith an oxygenating plasma.

In some embodiments, the improved deposition parameter is increased filmthickness. In some embodiments, the improved deposition parameter isdecreased film resistance. In some embodiments, the improved depositionparameter is increased uniformity. These improvements are relative to agraphene layer deposited by similar process parameters (e.g., reactants,temperature, plasma power, deposition time) on substrate surface whichhas not been treated with an oxygenating plasma.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the disclosure herein has been described with reference toparticular embodiments, those skilled in the art will understand thatthe embodiments described are merely illustrative of the principles andapplications of the present disclosure. It will be apparent to thoseskilled in the art that various modifications and variations can be madeto the method and apparatus of the present disclosure without departingfrom the spirit and scope of the disclosure. Thus, the presentdisclosure can include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method of forming a graphene layer, the methodcomprising: exposing a substrate surface comprising a dielectricmaterial to an oxygenating plasma, the dielectric material comprisingone or more of silicon, silicon nitride or glass; and exposing thesubstrate surface to a microwave surface-wave plasma comprisinghydrocarbon and hydrogen radicals to form a graphene layer.
 2. Themethod of claim 1, wherein the oxygenating plasma comprises O₂ or H₂O.3. The method of claim 1, wherein the microwave surface-wave plasma hasa peak power of less than or equal to 25 kW.
 4. The method of claim 1,wherein the microwave surface-wave plasma has a radical density ofgreater than or equal to 10¹² radicals/cm³.
 5. The method of claim 1,wherein the microwave surface-wave plasma has an energy of less than orequal to 10 eV.
 6. The method of claim 1, wherein a hydrocarbon gas anda hydrogen-containing gas are ignited to form the microwave surface-waveplasma comprising hydrocarbon and hydrogen radicals.
 7. The method ofclaim 6, wherein the hydrocarbon gas comprises one or more of methane,ethane, propane, butane, ethylene, propene, or acetylene.
 8. The methodof claim 1, wherein the substrate surface is maintained at a temperatureof less than or equal to 800° C.
 9. The method of claim 1, wherein thegraphene layer comprises 5 to 10 monolayers of graphene.
 10. The methodof claim 9, wherein the graphene layer is formed in a period of lessthan or equal to 15 minutes.
 11. The method of claim 1, wherein thegraphene layer has a resistance of less than or equal to 500 ohm/square.12. A method of forming a graphene layer, the method comprising:pretreating a substrate surface comprising a dielectric material byexposing the substrate surface to an oxygenating plasma, the oxygenatingplasma comprising O₂, the dielectric material comprising one or more ofsilicon, silicon nitride or glass; and exposing the substrate surface toa microwave surface-wave plasma comprising hydrocarbon and hydrogenradicals to form a graphene layer by igniting acetylene and hydrogengas, wherein the oxygenating plasma and the microwave surface-waveplasma have a peak power of less than or equal to 20 kW, the substratesurface is maintained at a temperature of less than or equal to 750° C.,the graphene layer comprises 5 to 10 monolayers of graphene and isformed in a period of less than or equal to 2 minutes.
 13. A method offorming a graphene layer, the method comprising: exposing a substratesurface comprising a dielectric material to an oxygenating plasma; andexposing the substrate surface to a microwave surface-wave plasmacomprising hydrocarbon and hydrogen radicals to form a graphene layer,the microwave surface-wave plasma having a radical density of greaterthan or equal to 10¹² radicals/cm³.
 14. The method of claim 13, whereinthe dielectric material comprises one or more of silicon, silicon oxide,silicon nitride or glass.
 15. The method of claim 13, wherein thedielectric material comprises one or more of silicon, silicon oxide,silicon nitride or glass.
 16. The method of claim 13, wherein themicrowave surface-wave plasma has a peak power of less than or equal to25 kW.
 17. The method of claim 13, wherein the microwave surface-waveplasma has an energy of less than or equal to 10 eV.
 18. The method ofclaim 13, wherein a hydrocarbon gas and a hydrogen-containing gas areignited to form the microwave surface-wave plasma comprising hydrocarbonand hydrogen radicals.
 19. The method of claim 18, wherein thehydrocarbon gas comprises one or more of methane, ethane, propane,butane, ethylene, propene, or acetylene.
 20. The method of claim 13,wherein the substrate surface is maintained at a temperature of lessthan or equal to 800° C.